@Misc{Altera,
  author = {Altera University Program},
  title  = {The 1st 5G Algorithm Innovation Competition-SCMA },
  file   = {online:http://www.innovateasia.com/5g/images/pdf/1st%205G%20Algorithm%20Innovation%20Competition-ENV1.0%20-%20SCMA.pdf:PDF},
  groups = {5G},}

@InProceedings{Cheng2015,
author    = {M. Cheng and Y. Wu and Y. Chen},
booktitle = {International Conference on Wireless Communications Signal Processing (WCSP)},
title     = {Capacity Analysis for Non-orthogonal Overloading Transmissions under Constellation Constraints},
year      = {2015},
pages     = {1-5},
abstract  = {In this work, constellation constrained (CC) capacities of a series of non-orthogonal overloading transmission schemes are derived in AWGN channels. All these schemes follow a similar transmission structure, in which modulated symbols are spread on to a group of resource elements (REs) in a sparse manner, i.e., only a part of the REs have nonzero components while the others are filled with zeros. The multiple access schemes follow this structure is called sparse code multiple access (SCMA) in general. In particular, a complete SCMA scheme would combine multi-dimensional modulation and the low density spreading (LDS) together such that the symbols from the same data layer on different REs are different but dependent. If the spread symbols are the same, it is a simplified implementation of SCMA and is called LDS. Furthermore, depending on whether the numbers of non-zero components for each data layer are equal or not, there are regular LDS (LDS in short) and irregular LDS (IrLDS), respectively. The paper would show from theoretical derivation and simulation results that the complete SCMA schemes outperform the simplified version LDS/IrLDS. Moreover, we also show that the application of phase rotation in the modulator can significantly boost the link performance of such non-orthogonal multiple access schemes.},
keywords  = {AWGN channels;code division multiple access;nonorthogonal overloading transmission capacity analysis;constellation constraint;AWGN channel;resource element;sparse code multiple access scheme;SCMA scheme;multidimensional modulation;low density spreading;nonorthogonal multiple access scheme link performance;code division multiple access;Nickel;Modulation;5G mobile communication;Multiaccess communication;Sparse matrices;AWGN channels;Simulation;SCMA;LDS;IrLDS;Constellation Constrained capacity;Non-orthogonal multiple access},
doi       = {10.1109/WCSP.2015.7341294},
month     = {Oct},}

@InProceedings{Zhang2016,
author    = {S. Zhang and K. Xiao and B. Xiao and Z. Chen and B. Xia and D. Chen and S. Ma},
booktitle = {International Conference on Wireless Communications Signal Processing (WCSP)},
title     = {A Capacity-based Codebook Design Method for Sparse Code Multiple Access Systems},
year      = {2016},
pages     = {1-5},
abstract  = {Sparse code multiple access (SCMA) is a novel non-orthogonal multiple access scheme, which exploits a multidimensional constellation based on the non-orthogonal spreading technique. The SCMA multi-user codebook design is the bottleneck of system performance and there is no design guideline from the perspective of capacity. In this paper, a novel SCMA codebook design scheme is proposed to maximize the sum rate, where we transfer the design of multi-dimensional constellation sets to the optimizing of series of 1-dimensional complex codewords. Specifically, a basic M-order pulse-amplitude modulation (PAM) is optimized and then the angles of rotation between the input 1-dimensional constellation and the basic M-PAM constellation can be obtained within a feasible calculation complexity to improve the sum-rate. Finally, the series of 1-dimensional complex codewords are combined to construct multi-dimensional codebooks based on Latin square criterion. Numerical results illustrate that the proposed codebook outperforms the existing codebook by 1.3 dB over AWGN channel and 1.1 dB over Rayleigh channel in terms of bit error rate (BER) performance.},
keywords  = {AWGN channels;error statistics;multi-access systems;pulse amplitude modulation;Rayleigh channels;capacity-based codebook design;sparse code multiple access systems;non-orthogonal multiple access scheme;non-orthogonal spreading;SCMA;multi-user codebook design;M-order pulse-amplitude modulation;PAM;Latin square criterion;AWGN channel;Rayleigh channel;bit error rate;BER;Design methodology;Modulation;Signal to noise ratio;NOMA;Uplink;Optimization;Receivers},
doi       = {10.1109/WCSP.2016.7752620},
ISSN      = {2472-7628},
month     = {Oct},}

@Article{SongWC2016,
author={G. Song and X. Wang and J. Cheng},
journal={IEEE Access},
title={Signature Design of Sparsely Spread Code Division Multiple Access Based on Superposed Constellation Distance Analysis},
year={2017},
volume={5},
pages={23809-23821},
abstract={Sparsely spread code division multiple access (SCDMA) is a non-orthogonal superposition coding scheme that allows concurrent communications between a base station and multiple users over a common channel. However, the detection performance of an SCDMA system is mainly determined by its signature matrix, which should be sparse to facilitate the belief propagation (BP) detection. On the other hand, to guarantee good maximum likelihood (ML) detection performance, the minimum Euclidean distance for the equivalent signal constellation after multi-user superposition should be maximized. In this paper, a code distance analysis is proposed for SCDMA systems with a finite number of users and spreading lengths. Based on this analysis, good signature matrices whose factor graphs have very few short cycles and possess large superposed signal constellation distances are designed. The proposed signature matrices have both good BP and ML detection performances. Moreover, their BP detection performances exactly converge to their ML detection performances with few iterations. It is worth pointing out that the proposed signature matrix design could be directly applied to the 5G non-orthogonal multiple access systems.},
keywords={channel coding;code division multiple access;interference suppression;matrix algebra;radio links;radio receivers;radiofrequency interference;signal detection;signature design;sparsely spread code division multiple access;superposed constellation distance analysis;nonorthogonal superposition coding scheme;concurrent communications;base station;multiple users;common channel;SCDMA system;belief propagation detection;minimum Euclidean distance;equivalent signal constellation;multiuser superposition;code distance analysis;spreading lengths;superposed signal constellation distances;ML detection performances;BP detection performances;signature matrix design;5G nonorthogonal multiple access systems;maximum likelihood detection performance;Multiaccess communication;Sparse matrices;Quadrature amplitude modulation;NOMA;Base stations;Complexity theory;Constellation diagram;Non-orthogonal multiple access;sparsely spread;signature design;code distance},
doi={10.1109/ACCESS.2017.2765346},
ISSN={2169-3536},}

@InProceedings{Klimentyev2017,
author={V. P. Klimentyev and A. B. Sergienko},
booktitle={European Wireless Conference},
title={SCMA Codebooks Optimization Based on Genetic Algorithm},
year={2017},
pages={1-6},
abstract={Sparse code multiple access (SCMA) is a nonorthogonal multiple access scheme based on joint modulation and spread spectrum procedure. This scheme allows to increase the number of active users inside a given time-frequency resource. Design of SCMA codebooks is a challenging problem. The paper considers the design of SCMA codebooks based on Genetic Algorithm (GA). In general case, mother constellation is not required for GA, and optimization is performed directly on the codebooks. We present the obtained structured codebooks containing two antipodal codeword pairs. Optimization was carried out to improve SCMA signal performance in additive white Gaussian noise (AWGN) channel by constraining the average energy of codewords. The obtained codebooks have minimum Euclidean distance equal to 0.87 (at unit average power of SCMA signal) and outperform known codebooks in AWGN channel with both Maximum Likelihood (ML) receiver or Message Passing Algorithm (MPA) detection. The comparison of existing and proposed codebooks is performed using computer simulation and union bounds. The asymptotic gain over the best known codebooks is 0.8 dB. As a result of the simulation, proposed codebooks demonstrate similar performance for ML and MPA detection algorithms. The proposed method is suitable for codebook design for other non-orthogonal schemes, e. g., Pattern Division Multiple Access (PDMA).},
doi={},
ISSN={},
month={May},}

@InProceedings{Wu2015,
author={Y. Wu and S. Zhang and Y. Chen},
booktitle={IEEE International Conference on Communications (ICC)},
title={Iterative Multiuser Receiver in Sparse Code Multiple Access Systems},
year={2015},
pages={2918-2923},
abstract={Sparse code multiple access (SCMA) is a novel non-orthogonal multiple access scheme, in which multiple users access the same channel with user-specific sparse codewords. In this paper, we consider an uplink SCMA system employing channel coding, and develop an iterative multiuser receiver which fully utilizes the diversity gain and coding gain in the system. The simulation results demonstrate the superiority of the proposed iterative receiver over the non-iterative one, and the performance gain increases with the system load. It is also shown that SCMA can work well in highly overloaded scenario, and the link-level performance does not degrade even if the load is as high as 300%.},
keywords={channel coding;iterative methods;receivers;iterative multiuser receiver;sparse code multiple access systems;novel nonorthogonal multiple access scheme;uplink SCMA system;channel coding;diversity gain;coding gain;OFDM;Decoding;Complexity theory},
doi={10.1109/ICC.2015.7248770},
ISSN={1550-3607},
month={June},}

@InProceedings{Klimentyev2016,
author={V. P. Klimentyev and A. B. Sergienko},
booktitle={Conference of Open Innovations Association and Seminar on Information Security and Protection of Information Technology (FRUCT-ISPIT)},
title={Detection of SCMA Signal with Channel Estimation Error},
year={2016},
pages={106-112},
abstract={Fifth generation wireless communication systems should support, among other things, very large number of simultaneous connections. To address this requirement, various schemes of non-orthogonal multiple access (NOMA) were proposed that allow to increase the number of simultaneously active users. One of NOMA schemes is sparse code multiple access (SCMA), where sparse multidimensional codewords allow to use iterative detecting algorithms with reasonable complexity. In the paper, SCMA detection is investigated in the presence of channel estimation error. Uncoded and turbo coded SCMA is analyzed. Uplink channel with Rayleigh flat block fading is assumed. Simulation results show that required accuracy of the channel estimation depends on the turbo code block length. For full utilization of turbo code error-correction capability with short blocks (40 bits) normalized variance of channel estimation error should be less than 10<sup>-3</sup>, the same value applies to the case of uncoded SCMA. For turbo code with long blocks (1024 bits), estimation can be less accurate, with normalized variance up to 10<sup>-2</sup>. With such channel estimation accuracy, power loss is about 0.6-0.7 dB compared with the case of perfect estimation. Two different types of codebooks have shown the same performance for coded SCMA, that leads to conclusion that codebook with more simple structure that provides less complexity of detection algorithm is a good candidate for use in SCMA schemes. The comparison with traditional orthogonal multiple access scheme with the same overall spectral efficiency is provided for both uncoded and coded SCMA systems. In case of coded system, SCMA scheme is shown to have smaller BER in the range of bit error probabilities below 10<sup>-4</sup>-10<sup>-5</sup> for long blocks. The power gain is 0.5-1 dB for long blocks and a few tenths of dB for short blocks.},
keywords={block codes;channel coding;channel estimation;error correction codes;error statistics;multi-access systems;Rayleigh channels;signal detection;turbo codes;SCMA signal detection;channel estimation error;fifth generation wireless communication system;nonorthogonal multiple access scheme;NOMA scheme;sparse code multiple access;sparse multidimensional codeword;iterative detecting algorithm;turbo coded SCMA analyzed;uncoded SCMA analysis;uplink channel;Rayleigh flat block fading;turbo code error-correction capability;BER;bit error probability;Channel estimation;Fading channels;NOMA;Complexity theory;Turbo codes;Estimation;5G mobile communication},
doi={10.1109/FRUCT-ISPIT.2016.7561515},
ISSN={2305-7254},
month={April},}